1. Field of the Invention
The present invention relates to an impeller of a circumferential current pump (so-called xe2x80x9cwesco pumpxe2x80x9d) used as an in-tank type fuel pump of an automobile and a method of forming the impeller.
2. Description of the Prior Art
An in-tank type circumferential current pump having an improved property for being mounted to a vehicle and having a low noise and a small pressure change has been conventionally used in a fuel pump for an electronically controlled type fuel injection apparatus of an automobile.
FIGS. 23 to 25 show a circumferential current pump 51 for an automobile. The circumferential current pump 51 shown in these drawings is placed within a fuel tank (not shown), and is structured such as to apply an energy to a fuel by a vane 54 formed on an outer periphery of an impeller 52 when the impeller 52 is rotated by a motor 53 so as to increase a pressure of the fuel flowing into a pump flow passage 56 from a fuel inlet port 55 and discharge the fuel having the increased pressure to an engine side from a fuel discharge port 57.
In the circumferential current pump 51 mentioned above, in order to maintain a pump efficiency and a discharge pressure in a desired state, it is necessary to set gaps w1 and w2 in a side of side surfaces 58a and 58b of the impeller 52 within a predetermined size so as to reduce a leaked flow amount. Further, in the circumferential current pump 51 mentioned above, since the impeller 52 is always in contact with the fuel within the fuel tank, a phenol resin or a PPS resin excellent in a solvent resistance is used as a material for the impeller 52, whereby the impeller 52 is formed in a desired shape in accordance with an injection molding.
However, when using the injection molded impeller 52 as it is, the sizes of the gaps w1 and w2 on the side surfaces 58a and 58b of the impeller 52 do not satisfy a desirable accuracy due to a surface accuracy of the side surfaces 58a and 58b of the impeller 52, so that desired pump efficiency and discharge pressure can not be obtained.
Accordingly, in the conventional circumferential current pump 51, a width of the impeller 52 is finished at a high accuracy by polishing both of the side surfaces 58a and 58b of the injection molded synthetic resin impeller 52 and a surface accuracy of both of the side surfaces 58a and 58b of the impeller 52 is finished at a high accuracy. Therefore, the conventional impeller 52 has a disadvantage that a process and labor for working is much and a producing cost is increased (a first prior art).
Further, as shown in FIG. 26, there has been proposed an impeller 52 structured such as to reduce a resistance applied to both of the side surfaces 58a and 58b in comparison with the first prior art in which a whole of both of the side surfaces 58a and 58b forms a seal portion, by forming an annular recess 60 in both of the side surfaces 58a and 58b, forming a first seal portion S1 in an outer peripheral side thereof and forming a second seal portion S2 in an inner peripheral side thereof (refer to Japanese Unexamined Patent Publication No. 7-151091). However, since the impeller 52 is structured such that two seal portions S1 and S2 are formed in such a manner as to be apart from each other in a radial direction, it is necessary to polish both of the side surfaces 58a and 58b after the injection molding, in the same manner as that of the prior art mentioned above. Accordingly, the impeller 52 shown in FIG. 26 also has a disadvantage that a process and labor is much and a producing cost is increased in the same manner as that of the prior art mentioned above (a second prior art).
Accordingly, the applicant of the present invention proposed an invention structured such that a recess portion 61 is formed in a center portion of both of the side surfaces 58a and 58b of the impeller 52, a gate 62 for injection is arranged in the recess portion 61 and a pressure adjusting hole 63 is formed as shown in FIG. 27, whereby the injection molded impeller 52 can be used as it is without being polished (Japanese Unexamined Patent Publication No. 9-158885 (a third prior art)). However, in correspondence to a high performance of a fuel pump in recent years, it has been desired to provide an impeller having a higher accuracy.
Accordingly, an object of the present invention is to provide an impeller for a circumferential current pump which can solve the disadvantages in the prior arts mentioned above, and a method of forming the same.
In accordance with a first aspect of the present invention, there is provided an impeller for a circumferential current pump which is provided with a plurality of vane grooves in an outer peripheral side of a synthetic resin disc-like member rotated by a motor and is rotatably received within a substantially disc-like space formed between a pump casing and a pump cover, wherein a recess portion having a predetermined radius around a center of rotation is formed on at least one of one side surface opposing to the pump casing of the disc-like member and another side surface opposing to the pump cover. Further, the structure is characterized in that a ratio (L/2t) between the sum (t1+t2=2t) of a gap (t1) between the one side surface and the pump casing and a gap (t2) between the another side surface and the pump cover, and a size (L=R0xe2x88x92Hxe2x88x92R1) obtained by subtracting a radial groove length (H) of the vane groove and a radial size (R1) of the recess portion from a radial size (R0) of the disc-like member satisfies a relation 66xe2x89xa6(L/2t). In this case, the recess portion includes a substantially disc-like recess portion around a center of rotation of the disc-like member and a substantially annular recess portion around a center of rotation of the disc-like member.
In accordance with the present invention having the structure mentioned above, since it is possible to make the size (L) of the side surface functioning as a seal portion as small as possible, it is possible to form the side surface functioning as the seal portion at a high accuracy only in accordance with an injection molding. Therefore, in accordance with the present invention, a polishing of the impeller side surface is not required, so that it is possible to reduce a process and labor for producing the impeller. Further, in accordance with the present invention, as mentioned above, since it is possible to form the side surface functioning as the seal portion of the impeller at a high accuracy, it is possible to make the gap sizes (t1 and t2) smaller than those of the third prior art.
In accordance with a second aspect of the present invention, there is provided an impeller for a circumferential current pump which is provided with a plurality of vane grooves in an outer peripheral side of a synthetic resin disc-like member rotated by a motor and is rotatably received within a substantially disc-like space formed between a pump casing and a pump cover. Then, the impeller for the circumferential current pump is structured such that a recess portion having a predetermined radius around a center of rotation is formed on at least one of one side surface opposing to the pump casing of the disc-like member and another side surface opposing to the pump cover, and a plurality of grooves extending in a radial direction within the recess portion are formed in a radial shape.
In accordance with the present invention having the structure mentioned above, a plurality of grooves are formed in a radial shape so as to reduce a solid portion in the recess portion, whereby a cooling efficiency at a time of injection molding can be increased, a cycle time for the injection molding can be reduced, and a deformation of a whole of the impeller due to a molding shrinkage (sink mark). Further, in accordance with the present invention, since a plurality of grooves are formed in a radial shape as mentioned above and the solid portions between the grooves function as a rib, it is possible to reduce a weight without reducing a rigidity of the impeller and it is possible to reduce a used amount of the synthetic resin material.
In accordance with a third aspect of the present invention, there is provided an impeller for a circumferential current pump as recited in the second aspect mentioned above, wherein a ratio (L/2t) between the sum (t1+t2=2t) of a gap (t1) between the one side surface and the pump casing and a gap (t2) between the another side surface and the pump cover, and a size (L=R0xe2x88x92Hxe2x88x92R1) obtained by subtracting a radial groove length (H) of the vane groove and a radial size (R1) of the recess portion from a radial size (R0) of the disc-like member satisfies a relation 66xe2x89xa6(L/2t).
In accordance with the present invention having the structure mentioned above, it is possible to obtain the effects of the first aspect and the second aspect in a combined manner.
In accordance with a fourth aspect of the present invention, there is provided an impeller for a circumferential current pump as recited in any one of the first to third aspects, wherein a shape between the vane grooves on a side surface of the disc-like member is substantially rectangular.
In accordance with the present invention having the structure mentioned above, the impeller can be easily released from the mold after the injection molding, whereby it is possible to prevent an inferior mold release and prevent the impeller from being deformed together with the mold release.
In accordance with a fifth aspect of the present invention, there is provided an impeller for a circumferential current pump as recited in any one of the first to third aspects, wherein a shape of the vane groove on a side surface of the disc-like member is formed in such a manner as to expand a groove width from an inner portion in a radial direction toward an outer portion, and a shape between the vane grooves is formed in a substantially trapezoidal shape in which a width is reduced from the inner portion in the radial direction toward the outer portion.
In accordance with the present invention having the structure mentioned above, the impeller can be more easily released from the mold after the injection molding than the invention described in the fourth aspect, so that it is possible to further effectively prevent the inferior mold release and prevent the impeller from being deformed together with the mold release.
In accordance with a sixth aspect of the present invention, there is provided an impeller for a circumferential current pump as recited in any one of the first to fifth aspects, wherein a corner portion in a bottom portion of the vane groove is beveled.
In accordance with the present invention having the structure mentioned above, the impeller can be easily released from the mold after the injection molding, whereby it is possible to reduce a deformation of the impeller and an inferior mold release at a time of releasing from the mold.
In accordance with a seventh aspect of the present invention, there is provided an impeller for a circumferential current pump as recited in any one of the first to sixth aspects, wherein a pressure adjusting hole extending through the another side surface from the one side surface is formed at an inner position in a radial direction from a position at which a ring gate for the injection molding is arranged, within the recess portion.
In accordance with the present invention having the structure mentioned above, an injected synthetic resin material is smoothly supplied to a portion of the impeller in which a surface accuracy is required. Further, a pin for forming the pressure adjusting hole is arranged within a metal mold for the injection molding, whereby a surface rough portion together with a weld phenomenon is received within the recess portion even when the weld phenomenon is generated, so that the surface accuracy of the impeller side surface is not deteriorated.
In accordance with an eighth aspect of the present invention, there is provided a method of forming an impeller for a circumferential current pump in which a plurality of vane grooves are formed in an outer peripheral side of a synthetic resin disc-like member and a recess portion having a predetermined radius around a center of rotation is formed on at least one of one side surface of the disc-like member and another side surface thereof. Further, the structure is characterized in that a ring gate for an injection molding is arranged at a position corresponding to the recess portion and a synthetic resin is injected into a cavity from the ring gate.
In accordance with the present invention having the structure mentioned above, a burr generated at a time of cutting the ring gate is received within the recess portion of the impeller, so that a surface accuracy of the impeller side surface is not deteriorated and it is possible to injection mold an impeller having a high accuracy.